The size distribution of unit particles of two New Zealand allophanes (An and Rh), in dilute (0.8% w/v) aqueous suspensions, has been determined by small-angle neutron scattering (SANS). In addition, the specific surface area of the samples was measured by ethylene glycol retention, and their morphology examined by high-resolution transmission electron microscopy (HRTEM). The SANS data indicate that although both allophanes are somewhat polydisperse, the average diameter of their unit particles is significantly different, being 56 and 43 Å for allophane-An and allophane-Rh, respectively. Consistent with this observation, the specific surface area of allophane-Rh (897 mVg) is appreciably greater than that of allophane-An (638 m2/g). Under the electron microscope, both samples appear as aggregates of hollow spherules but HRTEM did not clearly distinguish between the two allophanes in that the largest population of spherules had diameters near 50 Å. Because of the assumptions and uncertainties involved in the SANS and surface area measurements, the data must be discussed in terms of their respective ratios. On this basis, the spherule diameter ratio is of the same order of magnitude as the inverse ratio of specific surface area. The latter value is also in reasonably good agreement with the corresponding ratios of phosphate adsorption capacity and BET nitrogen areas, derived from earlier studies.

The present study investigated the anisotropy in the orientation of particles in synthetic swelling clay media prepared from the sedimentation of particle-sized fractions of vermiculite. The different size fractions (<0.1, 0.1–0.2, 1–2, and 10–20 μm) were chosen because they represent the wide range of particle sizes of swelling clay minerals encountered in natural environments. Small-angle neutron scattering (SANS) and neutron diffraction measurements allowed the characteristic scattering/diffraction features to be derived and the quantitative information about the particle orientation distributions along two directions with respect to the sedimentation plane to be extracted. The results obtained confirmed that the increase in particle size was associated with the development of a random orientation for the particles, whereas the hydration state had a negligible impact on the organization of the porous media. For finer vermiculite particles, the rocking curves demonstrated an anisotropy of the systems that is similar to those reported previously on natural montmorillonite minerals. This result suggests that the location of the layer charge has little or no impact on the anisotropy features of particle orientation. For the coarsest fraction (10–20 μm), quantitative information about the particle orientation revealed that the relative proportion of the isotropic contribution represents up to 85% of the material. The anisotropy in the 2D SANS patterns revealed a pore-network anisotropy that was consistent with the particle size.

An Fe–1 at.% Cu model alloy was examined by atom probe (3DAP) and small-angle neutron scattering (SANS) to verify the accordance of the gained results. The Fe-Cu alloy was heat-treated for various times at 500°C, forming Cu-rich precipitates within the Fe matrix. The chemical compositions of the precipitates and matrix found by 3DAP were used to calculate the magnetic scattering contrast. Additionally, a magnetic moment of the precipitates that contain a significant amount of Fe was taken into account for the calculation of magnetic scattering contrast. This in turn is used for the evaluation of the magnetic scattering curves gained by SANS. Both the 3DAP data as well as the scattering curves were analyzed with regard to radius, number density, and volume fraction of the precipitates as a function of aging time. The results yielded by both techniques are in good agreement and correspond to the development of the hardness of the alloy. Minor differences can be related to the cluster search algorithm used for the analysis of the 3DAP data as well as Fe overestimation based on different field phases.

We present a model for the skeletal muscle troponin-C (TnC)/troponin-I (TnI) interaction, a critical molecular switch that is responsible for calcium-dependent regulation of the contractile mechanism. Despite concerted efforts by multiple groups for more than a decade, attempts to crystallize troponin-C in complex with troponin-I, or in the ternary troponin complex, have not yet delivered a high-resolution structure. Many groups have pursued different experimental strategies, such as X-ray crystallography, NMR, small-angle scattering, chemical cross-linking, and fluorescent resonance energy transfer (FRET) to gain insights into the nature of the TnC/TnI interaction. We have integrated the results of these experiments to develop a model of the TnC/TnI interaction, using an atomic model of TnC as a scaffold. The TnI sequence was fit to each of two alternate neutron scattering envelopes: one that winds about TnC in a left-handed sense (Model L), and another that winds about TnC in a right-handed sense (Model R). Information from crystallography and NMR experiments was used to define segments of the models. Tests show that both models are consistent with available cross-linking and FRET data. The inhibitory region TnI(95–114) is modeled as a flexible β-hairpin, and in both models it is localized to the same region on the central helix of TnC. The sequence of the inhibitory region is similar to that of a β-hairpin region of the actin-binding protein profilin. This similarity supports our model and suggests the possibility of using an available profilin/actin crystal structure to model the TnI/actin interaction. We propose that the β-hairpin is an important structural motif that communicates the Ca2+-activated troponin regulatory signal to actin.

Understanding protein folding requires the determination of the configurational space accessible to the protein at different stages in folding. Here, computer simulation analysis of small angle neutron scattering results is used to probe the change in the distribution of configurations on strong denaturation of a globular protein, phosphoglycerate kinase, in 4 M guanidine hydrochloride solution. To do this atomic-detail ensembles of the unfolded protein chain are modeled and their scattering profiles compared with the experiment. The local conformational statistics are found to strongly influence the experimental intensity at scattering vectors between 0.05 and 0.3 Å−1. Denaturation leads to a reduction in the protein atom-pair distance distribution function over the ∼3–15 Å region that is associated with a quantifiable shift in the backbone torsional angle (φ,ψ) distribution toward the β region of the Ramachandran plot.